1. Field of the Invention
The field of the invention is that of data exchanges between a microprocessor and one or more remote memories in data processing systems.
2. Description of Related Art
Generally, the function of a microprocessor is to execute the instructions of programs contained in its memory space. This memory space is embodied by a local memory and possibly by various input-output registers. These instructions and the data required for their execution are accessible by the microprocessor using the addressing means of its memory space. However, considering the relatively long times required to access its entire address space, the microprocessor is usually equipped with a cache memory which is much faster, but whose content is limited to a certain number of extracts from the contents of the local memory and possibly from the various input-output registers. The cache memory is adapted to the address space of the microprocessor. Further details on the operation of cache memories may be found by referring to the following U.S. patents filed in the name of the "Assignee of the present invention", which describe devices for access to a memory by a processor:
The execution by the microprocessor of the instructions of programs contained in a memory space external to its own memory space raises the problem of the incompatibility of its cache memory to this external memory space. It is possible to provide, in a circuit for interfacing with the microprocessor, input-output registers inside the memory space of the microprocessor, in communication with the physical elements of the external memory space so as to provide direct access to the instructions and to the data required for their execution contained in these physical elements. However, if the physical elements of the external memory space are remote storage units, the latency in the exchanges runs the risk of considerably diminishing the performance of the microprocessor in its execution of programs.